The trial of a police officer who smashed open a car window before using an allegedly illegal lock knife to saw at the shattered glass has heard that it is “common practice” for officers to carry their own blades.

PC Joshua Savage is alleged to have “lost it” and used unlawful force when a driver refused to leave his car in Weedington Road, Queen’s Crescent.

Footage of the incident, which was filmed by the car’s sole passenger, was played to a jury at Southwark Crown Court this week.

The prosecution allege it was illegal for PC Savage to carry the multi-tool, with a blade of more than three inches that locked open. He had bought the tool himself and had not been authorised to carry it by the Metropolitan Police, the court heard.

But PC Savage said it is “common practice throughout the police”.

He said some officers had even been commended for their life-saving actions using multi-tools, which “implies organisational approval”.

The court heard officers have used knives to cut seat belts at the scene of accidents or remove ligatures from the necks of people who had tried to hang themselves.

PC Savage said: “Officers that are in roles which involve them protecting the public absolutely need to have a bit of kit like that.”

He added: “I wouldn’t be happy to work on a response team without a multitool.”

While he knew it would be illegal to carry off-duty, he believes it was permitted for him to use do so for work.

A colleague from Kentish Town police station, PC Philip Mansell, told the court that he estimates about one in five officers carries a self-bought knife.

“When I first joined the Met I spoke to a number of experienced officers who carry these tools with them.”

Martin Graves, a retired Met officer who helped develop the force’s guidelines on officer safety and use of force, said it was often necessary for officers to carry a knife.

“I carried one myself all the years I was on service,” he said.

Prosecuting barrister Jonathan Polnay told the jury that there was a debate around arming police with firearms and tasers, but added: “I don’t think anyone is suggesting that the police should be allowed to carry knives”.

He added: “We don’t have a knife-carrying police force and I don’t think PC Savage is going to suggest to you that this is a Met-authorised knife.”

The court had early heard that PC Savage and his colleague had mistakenly identified the driver, Leon Fontana, as another young man who was said to be “well known to police” and allegedly had a reputation for violence.

The footage, filmed by Mr Fontana, shows him repeatedly pleading with officers that they have got the wrong man.

Mr Fontana told the court that he felt “very threatened” and “very frightened” as PC Savage struck his car on September 16, 2016.

“I definitely wasn’t leaving my car,” he said. “I thought if I left that car I would have been in danger, certainly.”

Mr Polnay told the jury: “You might think it is not unfair to say that [PC Savage] comes across in that clip as a bully in uniform.”

In a witness statement, written at the time, PC Savage said he had been using “pre-emptive force” because he feared the vehicle may contain drugs or other offensive weapons that may be used against himself or his colleagues.

He denies charges of assault, destroying property and carrying an illegal blade.